The new Showtime series, "Masters Of Sex," chronicles the real life of pioneering sex researchers William Masters and Virginia Johnson. Their studies in the 1950s, '60s, and '70s, on top of previous work by Alfred Kinsey, changed American attitudes about sex at a time when masturbation was discouraged, oral sex between a husband and wife was illegal in some states, and homosexuality was considered a mental illness.

Our understanding of sex has matured over the last half-century, but none of that would have been possible without these groundbreaking findings from the earliest sex experts.

1. There are four phases of human sexual response — Masters and Johnson are widely recognized for their theory on the four stages of sexual response: excitement, plateau, orgasm, and resolution. The "human sexual response cycle" was published in their 1966 book "Human Sexual Response."

2. Women are capable of multiple orgasms — In studying the sexual response cycle of men and women, Masters and Johnson learned that women were capable of multiple orgasms after the resolution phase. The team quashed the "idea that women were not as sexually voracious as men" by claiming that "women could achieve five or six orgasms in as many minutes, while men had to leave the field for a 'refractory' period of an hour after every performance," The Telegraph writes.

3. Homosexuality is not a mental illness — In a 1979 book, Masters and Johnson debunked the idea that homosexuality was a mental illness (though controversially claimed to have successfully "converted" 70% of men and women who were dissatisfied with their homosexuality). Until 1973, homosexuality was classified as a mental disorder by the American Psychiatric Association.

4. Masturbation does not make people sick or cause insanity — Before the 20th century, most American physicians regarded masturbation as a "dangerous" sexual act that could cause illness.

According to "Sex and Human Loving," published in 1988 by Masters and Johnson, masturbation owes its bad reputation to a Swiss doctor, S. Tissot, who believed masturbation was a "particularly 'dangerous' form of sex because it was convenient and could be started during the vulnerable years of childhood, and because the masturbates guilt over his or her sinfulness further irritated the nervous system and made it more susceptible to damage."

They add: "By the time Tissot's notions had crossed the Atlantic to America, the average doctor was quite willing to believe that masturbation caused insanity, epilepsy, acne, weight loss, decreases mental capacity, weakness, lethargy, and — the ultimate punishment — early death." Masters and Johnson put this myth to bed.

5. Most men masturbate — Master and Johnson's research confirmed Kinsey's earlier findings: Masturbation is common. In his 1948 book, "Sexual Behavior in the Human Male," Kinsey found that 92% of men masturbated.

6. Actually, everyone masturbates — In 1953, Kinsey published his second volume, "Sexual Behavior in the Human Female," in which he reported that 62% of women said they had masturbated.

7. Americans are more sexually adventurous than previously thought — Kinsey recognized that most sexual acts that were frowned upon were regularly taking place behind closed doors. For example, he reported that 48.9% of married couple had engaged in oral sex, 11% of married males had had anal sex, and nearly half of married females slept naked. He also found that around half of married men had had extramarital affairs and 69% of white men paid to have sex with prostitutes.

8. Sex before marriage is not uncommon — Kinsey reported that between 67-98% of men had had premarital sex, depending on socioeconomic status, and around 50% of women had engaged in premarital sex.

9. Women peak sexually in their 30s — According to Kinsey, men reach their sexual peak before age 20, whereas women hit their sexual prime in their early-30s. Kinsey's research was based on orgasm frequency and probably corresponded to hormonal levels (i.e. men are easily aroused during their teenage years because of high testosterone levels and women's estrogen levels fall off at menopause around age 50). Today the idea that everyone reaches their sexual peak at the same age is seen as outdated since other physical and emotional factors must be considered.

10. A quick treatment for sexual dysfunctions — Before 1970, sexual dysfunctions like premature ejaculation or impotence were only thought treatable with long-term psychotherapy. Masters and Johnson developed an intense therapy program that involved just two weeks of daily treatment. No drugs or surgery were involved. The therapy sessions were attended by couples — not individuals — where the man and woman learned how to communicate about their problems in the bedroom. This method had an 80% success rate.

11. There is no actual age when sexual abilities disappear — Masters and Johnson were the first to conduct research on how older adults perform during sex. They found that women and men in their 70s were still able to orgasm.